Stimulation of tissue of a subject by applying an electrical potential to the tissue is well known in the medical art. Herein, in the specification and in the claims, tissue is to be understood as comprising muscle and/or nerve of a subject. Levels and type of stimulation used depend on a number of factors, such as whether the stimulation is applied externally, and the desired effect of the stimulation. When the tissue is stimulated directly, by one or more electrodes implanted in the tissue, levels of stimulation needed to achieve a specific desired effect are typically orders of magnitude less than the levels needed if the tissue is stimulated externally and/or indirectly. Devices for direct tissue stimulation, such as cardiac pacemakers, are typically implanted into the subject, and typically rely on an internal battery for producing their pulses.
Different types of pulses are known in the art for producing muscle stimulation. In the specification and in the claims, a biphasic pulse is assumed to be a pair of pulses having alternating positive and negative potentials, the biphasic pulse being able to stimulate the tissue; a mono-phase pulse is assumed to be a single uni-directional pulse which is able to stimulate the tissue; and alternating pulses are assumed to comprise a sequence of mono-phase pulses having alternating positive and negative potentials, each mono-phase pulse being able to stimulate the tissue. Typically, a time period between the pair of pulses comprising a biphasic pulse is of the order of 500 μs; a time period between sequential alternating pulses is of the order of 25 ms.
U.S. Pat. No. 5,391,191, to Holmstrom, whose disclosure is incorporated herein by reference, describes an implanted device for tissue stimulation. The device incorporates a current sensing mechanism which is applied to reduce tissue polarization, electrolysis effects, and detect tissue reaction. The device is implemented to deliver biphasic pulses, as well as a mono-phase pulses. Both types of pulses are used for stimulation; to reduce energy consumption, the device implements the mono-phase pulses.
It will be appreciated that efficiency in battery utilization in implanted devices is an important consideration, in order to increase battery life before recharging and/or replacement of the battery is required.
Anodal break excitation, also known as anode break excitation, may occur at an anode if tissue stimulation is abruptly halted. Such excitation is typically an undesired side effect of the tissue stimulation, and methods to reduce or eliminate the effect have been sought.